PHYSICS PAPER 1 (THEORY)(Three hours)(Candidates are allowed additional 15 minutes for only reading the paper.They must _OT start writing during this time.)---------------------------------------------------------------------------------------------------------------------Answer all questions in Part I and six questions from Part II, choosing two questionsfrom each of the Sections A, B and C.All working, including rough work, should be done on the same sheet as, and adjacent to,the rest of the answer.The intended marks for questions or parts of questions are given in brackets [ ].(Material to be supplied: Log tables including Trigonometric functions)A list of useful physical constants is given at the end of this paper.--------------------------------------------------------------------------------------------------------------------- PART I (20 Marks) Answer all questions.Choose the correct alternative (a), (b), (c) or (d) for each of the questions given below: [ 5 ](i) Two point charges 17.7 C and -17.7C, separated by a very small distance, arekept inside a large hollow metallic sphere. Electric flux emanating through thesphere is:(a) 2 106 Vm(b) -2 106 Vm(c) Zero(d) 4 106 Vm(ii)unit of electrical conductivity is:(a) Ohm m(b) Ohm^-1-m(c) Ohm^-1-m^-1(d) Mho-m(iii)the relation between dielectric constant K and temperature is that they are:(a)inversely proportional(b)directly proportional(c)equal(d) none of these(iv)type of field produced by stationary proton is:(a) Electric field(b) Magnetic field (c)electromagnetic field (d)none of these(v)a bar magnet of moment M and length l is cut in 2 equal parts each of length L/2.The magnetic moment of each part will be(a)M(b)M/4;(c)root(2)M;(d)M/2;B. Answer all questions given below briefly and to the point:(i), A dielectric slab of relative premittivity (i.e. dielectric constant ) 6 is introducedbetween the two plates of an 8F air capacitor, in order to completely occupy thespace between the two plates. Find the new capacitance of the capacitor.(ii).why a high resistance wire is connected in series to the coil of the voltmeter.(iii). What is the ratio P1: P2 of electric power deveoloped in R1 and R2 shown inFigure 1 below? R2=9 ohm: r1=6 ohm?Figure 1:

(iv). State two conditions which must be satisfied in order ito apply Tangent law inMagnetism(v).Name the two conservation laws implied in kkirchoffs laws for electric circuits.(vi).Free electrons always keep on moving in a conductor but experience no force when conductor is placed in a magnetic field.why? (vii). What type of wave front is associated with a line source of light?(viii). Out of the following, which one cannot be the charge of a body?+8.010-19C,-3.210-19C, 2.410-19C, or 6.410-19C(ix). Why is the core of transformer made of soft laminated iron?(x). What do u mean by term time constant of L-R circuit?(xi). State one advantage of a.c over d.c.(xii). When does a LCR series circuit have minimum impedance?(xiii).why is a choke coil preferred over a resistor to adjust the current in the ac circuit?(xiv). What is transformation ratio?(xv).why is soft iron used in the core of a transformer? PART II (50 Marks) Answer six questions in this part, choosing two questions from each of the Sections A, B and C. SECTIO' A Answer any two questions:Question 2(a)Figure 2 below shows an electric dipole AB of length l kept in a uniform electricfield E: (i) Show the electrostatic force acting on each of the charges forming the dipole.(ii) Hence, obtain an expression for the torque acting on the dipole. 2 mrk(b) Two plates of a charged parallel plate capacitor are pulled apart with the help ofinsulating handles, till their separation is doubled.Compare the new electrostatic potential energy of the capacitor with the old.[3](c) In Figure 3 below, find the reading of the voltmeter(V), having a resistance of 2000 ohm? 3 marks

Question 3:(a). Obtain the relation : r1/r2=r3/r4 for a wheatstone bridge.( 3) (b) Apply Kirchoffs Laws to determine the currents I1 and I2 in the circuit shown in Figure 4 below: 3 marks

(c) A coil of n turns is rewinded into 3n turns..Find the ratio of magnetic fields produced in the two cases , if the amount of current in the coil remains same. 3 marksQuestion 4:

(a) Using Amperes Circuital Law and with the help of a labelled diagram, show that magnetic flux density B at a distance r from a long straight conductor is given by:B =oI/2r. 3 marks(b) Obtain the relation for the current I=I0 sin (wt-/2) for a pure inductor across which an a.c of emf E=E0 sin wt is applied. 3

(c)with the help of appropriate diagram derive the relation e=Blv. For the motional emf produced in a wire of length l, moving with a velocity v, perpendicular to a unform magnetic field. 3 marks SECTION : B Answer any two questionsQuestion 5:(a) Show that the radius of a charged particle entering perpendicularly in a magnetic field is directlyproportional to its momentum.[3](b) An electric current of 0.25 A flows in a loop of radius 2.0 cm.calculate the magnitude of magnetic dipole moment of the dipole formed? 3 marks(c) What causes the core of the transformer to get heated up under operation? 2 marks

Question 6:

(a) Derive the power factor expression for LCR circuit.[3](b) Explain the mechanism of a choke coil. [3](c) What is gauss law in electrostatics? [2]

Question 7:

(a) 64 equal drops of mercury at v=10 volt each are combined to form a big drop .Find the potential in the big drop. 3 Draw a labelled diagram of a potentiometer circuit used to measure (b) internal resistanceof a cell. In this experiment, what is the expression for the internal resistance r? 3 marks(b) The resistance of a galvanometer is 50.It is converted into:(i)a voltmeter using a 10k resistor. 1(ii) an ammeter using a 10 m resistor. 1 Calculate the resistance of the voltmeter and the ammeter to an accuracy of 3 significant figure only.